Basic materials get the job done: Roofing caulk, galvanized roofing nails, tin snips, and step flashing (either flat or prebent).
Installing step flashing correctly is one of the first things I teach a new member of my crew. The first rule of flashing is that water runs downhill. The second rule of flashing is that sometimes rule No. 1 isn’t the whole truth and that water also runs uphill, as when it wicks up inside debris or backs up behind ice. For this reason, I like to lap all flashing by at least 2 in.
It’s important to remember that a building always is moving. If you nail step flashing to the wall and to the roof, you’re asking for trouble. Most of the time, I like to avoid putting any extra holes in the roof surface, so I nail step flashing to the sidewall only, where both the next piece of flashing and the siding will cover the nail head. The bottom corner, where you start the course of flashing, is made from two pieces of bent step flashing lapped over each other and caulked in place.